To whom he wrote letters three days ago?
三天前他给谁写信来着?
write a letter to sb.
如果要提问这个sb的话,要用to whom,而不是to who
同样的道理,
To whom you're talking to
你在和谁讲话?
Who you're talking?
你们在谈论谁?
选择题是c
Helen doesn't do well in Music
海伦音乐学的不好
doesn't do well学的不好,干得不好,固定搭配